Setting environment variables in the conda enviroment

[JoranAngevaare]

To increase the re-usability of the containers, it would be good to set the environment variables into the conda environment. This would make e.g. sourcing the container to a jupyter hub much easier (see this thread: https://xenonnt.slack.com/archives/C016UJZ090B/p1662896046434129)

There are two methods that should work:

1. https://conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html#setting-environment-variables
2. https://docs.conda.io/projects/conda-build/en/latest/user-guide/environment-variables.html#inherited-environment-variables

[jmosbacher]

An alternative would be to have a python script that is pointed to by PYTHONSTARTUP env variable and it sets up the environment if its not already setup e.g. env not activated via setup.sh